This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The broad long-term objective of this project has been to develop members of the Plasmodium vivax merozoite surface protein-3 (PvMSP-3) and PvMSP-9 recombinant proteins as candidate malaria vaccine products. This laboratory originally identified, expressed, and characterized these proteins and their potential as malaria vaccine candidates. We have identified and characterized additional members of the PvMSP3 family (total of eleven genes) and recombinant products representing each gene have been produced for biochemical characterization. The recombinant products were expressed in a prokaryotic system and have been used to produce polyclonal rabbit antisera which recognize each PvMSP3 protein. In keeping with our objective to evaluate the native immune response in humans, five recombinant products representing the PvMSP3 alpha (PvMSP-3a) protein were produced, purified and tested. Finally, the same five products representing the PvMSP3 alpha (PvMSP-3a) protein were tested for safety, immunogenicity and efficacy in Saimiri boliviensis monkeys. These primates are susceptible to P. vivax infections and can serve very well as a direct challenge model. While the challenge was very reliable, in support of the model system for testing of P. vivax blood stage vaccines, no protection was detected. This project has had a no cost extension, and these results are being prepared for publication, along with a paper on the gene and protein expression of the large MSP3 family. Additional studies on the naturally acquired and vaccine induced immune response to these antigens are also being completed by collaborators in Brazil and Papua New Guinea.